JP5667368B2 - Plasma processing equipment - Google Patents

Description

  The present invention relates to a plasma processing apparatus for plasma processing a substrate to be processed.

  Substrates used in the manufacture of semiconductor devices such as semiconductor memories and logic LSIs tend to be increased in diameter to improve productivity, and the most advanced semiconductor devices such as semiconductor memories use a silicon substrate having a diameter of 300 mm. Has become the mainstream. Furthermore, there is an opinion that a silicon substrate with a diameter of 450 mm is necessary, and it is thought that the trend of increasing the substrate diameter will continue. Although a plasma processing apparatus is used in the manufacturing process of these semiconductor devices, it is necessary to perform uniform plasma processing on the substrate to be processed, and the technical difficulty associated with increasing the diameter of the substrate to be processed tends to increase. .

  In order to perform uniform plasma processing on the substrate to be processed, the distribution of plasma characteristics such as plasma density and temperature in the vicinity of the substrate to be processed is important, and the technology to optimize the plasma distribution from the viewpoint of uniform plasma processing Is important.

  The plasma processing apparatus that generates plasma by microwave power has the characteristics that it can generate high-density plasma even under low pressure, and the plasma distribution can be easily controlled by adjusting the static magnetic field distribution in combination with the static magnetic field. Widely used in the manufacture of semiconductor devices. In response to the above-mentioned trend of increasing the diameter of the substrate, it is important to control the plasma distribution in the microwave plasma processing apparatus. However, microwaves have a wavelength as short as a few centimeters to several tens of centimeters, and the distribution of microwaves is easy to change with dimensions on the same order as the wavelength. The microwave distribution can be optimized to obtain a uniform plasma treatment over a wide range. It tends to be difficult.

  A conventional example of a plasma processing apparatus for generating plasma using microwaves is shown in FIG. As shown in FIG. 1, from the viewpoint of axial symmetry of plasma processing, a transmission path such as a waveguide for supplying microwave power to the processing chamber is often connected to the center of the processing chamber. Therefore, the microwave power often becomes high near the center of the processing chamber. Further, since plasma is lost on the wall surface of the processing chamber, the density tends to increase near the center away from the wall surface. Because of these effects, the density is often high near the central axis even on the substrate to be processed, and the plasma density distribution tends to be a convex distribution in many cases.

  Note that propagation characteristics of the microwave propagating in the circular waveguide, such as the electromagnetic field distribution inside the waveguide and the wavelength in the tube, have been clarified, and are described in Non-Patent Document 1, etc.

Masamitsu Nakajima, “Microwave Engineering”, Morikita Publishing

  In the above-described prior art, the plasma density distribution on the substrate to be processed tends to be a convex distribution that is high in the central portion and low in the peripheral portion, and the plasma processing characteristics tend to show non-uniformity corresponding to the convex distribution of the plasma density distribution.

  The problem to be solved by the present invention is to provide a plasma processing apparatus capable of relaxing the convex distribution tendency of the plasma density distribution and obtaining uniform plasma processing characteristics on the substrate to be processed.

A plasma processing apparatus according to the present invention includes a circular waveguide through which a microwave electric field propagates, and a cylindrical cavity having a diameter larger than that of the circular waveguide. And a plasma processing chamber which is disposed below the cavity and in which an electric field propagated to the cavity is supplied to form plasma, and the substrate to be processed disposed in the plasma processing chamber is A plasma processing apparatus for processing using plasma, wherein the ridge is arranged in an annular shape above the cavity to which the circular waveguide is connected, and is formed on the ceiling of the columnar cavity. A plurality of ridges arranged around the axis at a position where the electric field is weak. The lower end of the circular waveguide and the upper part of the cavity are connected to each other, and the cross section whose diameter is expanded downward is tapered and connected to the cavity. and a lower end a tapered waveguide diameter is smaller than the diameter of the cavity, of the tapered waveguide at the weak position of the tapered waveguide is a the hollow portion inside of the upper to be connected field A ridge arranged in an annular shape around the axis can also be provided.

  According to the present invention, by using the microwave three-dimensional circuit system, the distribution of the microwave electromagnetic field in the processing chamber is made uniform, so that the plasma processing uniformity is improved.

FIG. 1 is a schematic diagram illustrating the configuration of a conventional etching apparatus using microwaves. FIG. 2 is a schematic diagram showing the electric field distribution analysis result of the conventional circular waveguide and cavity. FIG. 3 is a schematic diagram showing a result of electric field distribution analysis of a conventional circular waveguide and a cavity. FIG. 4 is a schematic diagram showing the electric field distribution of the hollow portion provided with the circular waveguide and the ridge according to the first embodiment of the present invention. FIG. 5 is a schematic diagram showing an electric field distribution of a cavity portion provided with a ridge using a taper for connection between the circular waveguide and the cavity portion according to the second embodiment of the present invention. FIG. 6 is a graph showing the plasma density measurement results of the present invention and the conventional example.

  A plasma etching apparatus using the present invention will be described with reference to FIGS. 1 to 6 as an embodiment of the present invention.

  As a conventional example, FIG. 1 shows a schematic diagram of a plasma etching apparatus using a microwave. Microwaves oscillated from the microwave source 101 are transmitted using the rectangular waveguide 103 and brought to the circular waveguide 105 by the circular-rectangular converter 104.

  The automatic matching machine 102 can adjust the load impedance to automatically suppress the reflected wave. As the microwave source, a magnetron having an oscillation frequency of 2.45 GHz was used. An isolator 119 was used to protect the microwave source. The circular waveguide 105 is connected to the cavity 106. The cavity 106 has a function of adjusting the microwave electromagnetic field distribution to a distribution suitable for plasma processing. Below the cavity 106 is a plasma processing chamber 110 through a microwave introduction window 107 and a shower plate 108.

  Since the shower plate 108 is directly exposed to the plasma generated in the plasma processing chamber 110, a material that has high plasma resistance and does not adversely affect the plasma processing is desirable. As a material for the microwave introduction window 107 and the shower plate 108, quartz was used as a material that efficiently transmits microwaves and keeps the plasma processing chamber airtight. A minute gap (not shown) is provided between the microwave introduction window 107 and the shower plate 108, and gas is supplied from a processing gas supply system 109 used for plasma processing. The shower plate 108 is provided with a plurality of fine gas supply holes (not shown) to supply the processing gas to the plasma processing chamber 110 in a shower shape.

  A substrate electrode 112 for placing a substrate to be processed 111 is installed in the plasma processing chamber 110. A bias power supply 114 is connected to the substrate electrode 112 via an automatic matching machine 113 in order to supply bias power to the substrate 111 to be processed. A frequency of 400 kHz was used as the frequency of the bias power source.

  A static magnetic field generator 115 is provided around the plasma processing chamber 110, and a static magnetic field can be applied to the plasma processing chamber 110. When the electron cyclotron resonance phenomenon, in which the microwave power is resonantly absorbed by electrons when the electron cyclotron frequency matches the microwave frequency, plasma is generated even in a high vacuum region where it is usually difficult to generate plasma. It becomes possible, and there is an effect that a region where plasma treatment can be performed is expanded.

  In addition, by applying a static magnetic field to the plasma processing chamber, plasma loss is suppressed and plasma ignitability is enhanced, and by adjusting the distribution of the static magnetic field, the plasma generation region and diffusion are controlled to control the plasma distribution. be able to.

  By controlling the plasma distribution, it is possible to control the uniformity of plasma processing performed on the substrate 111 to be processed. When the microwave frequency is 2.45 GHz, the magnitude of the static magnetic field that causes electron cyclotron resonance is 0.0875 Tesla.

  In this case, in order to utilize the electron cyclotron resonance phenomenon, it is necessary to generate a static magnetic field of 0.0875 Tesla in the plasma processing chamber, and a static magnetic field capable of generating a static magnetic field of this magnitude in any place in the processing chamber. It is desirable to use a magnetic field generator. A multistage electromagnet was used as a static magnetic field generator. By using a multi-stage electromagnet, there is an effect that the adjustment of the static magnetic field distribution and the size can be easily controlled by the current flowing through the electromagnet.

  The plasma processing chamber 110 is evacuated by a vacuum exhaust pump 118 connected through a valve 116 and a conductance variable valve 117. As the vacuum exhaust pump 118, a turbo molecular pump whose exhaust side was exhausted by a rotary pump was used. The pressure in the plasma processing chamber 110 is monitored by a pressure gauge 120. There is provided a mechanism for maintaining a constant pressure by automatically controlling the exhaust speed for exhausting a gas such as a gas supplied by the processing gas supply system 109 or a gas generated during the etching process using a conductance variable valve.

  By using a circularly polarized wave generator in combination with the circular waveguide portion of the circular-rectangular converter 104, the microwave can be circularly polarized to improve the axial symmetry of processing. In addition, it is known that the characteristic of propagation and absorption to plasma differs depending on the direction of rotation of circularly polarized waves. In order to effectively cause the electron cyclotron resonance phenomenon, it is necessary to use circularly polarized waves that rotate in a direction in which electrons are always accelerated by a microwave electric field. When circularly polarized waves in this direction are used, microwave power can be more efficiently absorbed by electrons.

  In the apparatus shown in FIG. 1, when the plasma density distribution on the substrate electrode was measured, it was found that the density tends to be a convex distribution with a high density near the center and a low density near the center. In order to investigate the cause of the convex distribution of the plasma density distribution, the distribution of the microwave electromagnetic field radiated from the connection between the circular waveguide and the cavity was investigated. The results are schematically shown in FIGS.

  3 is a cross-sectional view taken along the connection surface between the circular waveguide and the cavity, and FIG. 2 is a cross-sectional view taken along the y-axis in FIG. 2 and 3, electric field vectors are shown. In FIG. 2, the direction of the electric field vector is parallel to the paper surface, and in FIG. 3, it is perpendicular to the paper surface. The analysis was performed on the outlet side of the cavity 202 on the assumption that microwaves are emitted into free space. The analysis was performed by solving Maxwell's equations by the finite element method. The circular waveguide 201 is supplied with microwaves in the TE11 mode, which is the lowest order mode of the circular waveguide.

  As for the microwave propagating in the circular waveguide, propagation characteristics such as the electromagnetic field distribution inside the waveguide and the wavelength in the tube have been clarified, and are described in the above non-patent documents.

  The diameter of the circular waveguide 201 was set to a size that allows transmission only in the circular waveguide TE11 mode. With reference to FIG. The electric field vector 203 is schematically indicated by an arrow. It was found that there was a surface wave-like electric field 204 along the connection surface of the circular waveguide 201 of the cavity 202 and an electric field 205 radiated inside the cavity 202. The surface wave-like electric field 204 has a tendency that the peak of the standing wave gradually decreases from the center toward the outside, which is considered to be one of the causes of the increase in density near the center.

  With reference to FIG. The electric field vector distribution at the connection surface between the circular waveguide and the cavity is displayed, and only the surface wave electric field in FIG. 2 is highlighted. It can be seen that standing waves of surface waves are distributed in the y-axis direction from the central axis. The positions of the antinodes and nodes of the standing wave are located at substantially the same radius with respect to the central axis.

  A structure for suppressing the surface wave-like electric field 204 was examined. FIG. 4 schematically shows the result. In order to suppress the surface wave-like electric field 204, an annular ridge 301 was provided at the top of the cavity. The ridge 301 is disposed at a position where the original surface wave electric field 204 (indicated by a broken arrow in FIG. 4) generated when the ridge 301 is not provided is weakened. Ridge was analyzed as a perfect conductor.

  In general, an electric field concentrates on a portion having a large curvature such as the tip of the ridge 301, and the electric field tends to hardly enter a portion corresponding to the bottom of the groove between the ridges. By utilizing this property, an attempt was made to suppress the surface wave electric field 204 by disposing the groove between the ridges at a position where the original surface wave electric field 204 is strong and disposing the ridge tip at a weak position. As a result of the analysis, it was found that the surface wave electric field can be suppressed.

  As described above, the surface wave-like electric field could be suppressed by the ridge 301, but the electric field radiated inside the cavity was not significantly affected by the installation of the ridge. The electric field is concentrated on the central axis at a position close to the circular waveguide in the cavity, and it was thought that this effect needs to be mitigated. FIG. 5 shows the proposed structure. A taper 401 is provided between the circular waveguide and the cavity.

  The taper 401 can suppress the disturbance of the TE11 mode distribution of the circular waveguide and increase the diameter. Disturbances in the distribution of the circular waveguide TE11 mode can be suppressed when the taper opening angle is small and the taper lower diameter is large, but there is a drawback that the apparatus becomes large. When the diameter of the taper lower part is as large as the diameter of the cavity, there is no room for generating a surface wave electric field, and there is a case where installation of the ridge is unnecessary or there is no room for installation of the ridge.

  In addition, even when only a taper without a ridge is provided, there is an effect of expanding the circular waveguide TE11 mode, which is effective in suppressing the central concentration of the microwave electric field. As mentioned above, the analysis result that microwave radiation was possible in the low-order mode with few abdominal nodes by taper or ridge was obtained.

  When the taper opening angle is reduced and the diameter on the taper lower side is increased, the disturbance of the distribution given to the circular waveguide TE11 mode can be suppressed. However, if priority is given to suppression of distribution disturbance, there is a drawback that the taper increases and the apparatus becomes larger. In this example, priority was given to downsizing of the apparatus, the taper opening angle shown in FIG. 5 was set to 60 degrees, and the diameter on the lower side of the taper was set to 43% of the diameter of the cavity.

  An etching apparatus to which the structure using the taper and ridge shown in FIG. 5 was applied was manufactured, and the plasma density distribution on the electrode was measured. A circularly polarized microwave was used by applying a circularly polarized wave generation mechanism to the circular waveguide part. The results are shown in FIG. For comparison, the results of the conventional example measured under the same conditions shown in FIG. 1 are also shown. Although it was a convex distribution in the conventional example, it can be seen that the present invention has a concave distribution.

DESCRIPTION OF SYMBOLS 101 Microwave source 102 Automatic matching machine 103 Rectangular waveguide 104 Circular rectangular converter 105 Circular waveguide 106 Cavity resonance part 107 Microwave introduction window 108 Shower plate 109 Processing gas supply system 110 Plasma processing chamber 111 Substrate 112 Substrate Electrode 113 Automatic matching machine 114 Bias power supply 115 Static magnetic field generator 116 Valve 117 Variable conductance valve 118 Vacuum exhaust pump 119 Isolator 120 Pressure gauge 201 Circular waveguide 202 Cavity 203 Microwave electric field vector 204 Surface wave electric field 205 Cavity Electric field radiated inside 301 Ridge 401 Taper

Claims (2)

A circular waveguide through which a microwave electric field propagates, a cylindrical hollow portion connected to the lower portion of the circular waveguide and having a larger diameter than the circular waveguide, and a lower portion of the hollow portion A plasma processing chamber in which an electric field that is disposed and propagated to the cavity is supplied to form a plasma, and a substrate to be processed disposed in the plasma processing chamber is processed using the plasma A device,
A ridge arranged in an annular shape above the cavity to which the circular waveguide is connected, and arranged around the axis at a position where the electric field is weak formed on the ceiling of the columnar cavity. A plasma processing apparatus having a plurality of ridges. A circular waveguide through which a microwave electric field propagates, a cylindrical hollow portion connected to the lower portion of the circular waveguide and having a larger diameter than the circular waveguide, and a lower portion of the hollow portion A plasma processing chamber in which an electric field that is disposed and propagated to the cavity is supplied to form a plasma, and a substrate to be processed disposed in the plasma processing chamber is processed using the plasma A device,
The lower end portion of the circular waveguide, which is disposed between the lower end portion of the circular waveguide and the upper portion of the cavity portion, has a tapered cross section with a diameter extending downward, and is connected to the cavity portion. and diameter tapered waveguide is smaller than the diameter of the cavity, axis of the tapered waveguide at the weak position of the electric field the tapered waveguide is a the hollow portion inside of the upper to be connected A plasma processing apparatus comprising a ridge arranged in an annular shape.

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